I would like to connect my DirecTV satellite box to the internet using my household wifi. This would allow me to program the box remotely and download movies late at night. A wireless ether-net adapter (won't accept usb) will cost about $100, which I'd rather not spend. It's on another floor so wiring would be a real hassle. I have an old, but functioning, 802.11b wireless router. How do I set it up to behave like a wireless adapter so it would connect to my main wireless router (802.11b/g)?

Go in to the setup and turn off the DHCP server (so it doesn't conflict with the DHCP being handed out by your main router). Then you need to try to get your router in to a wireless client mode - it may not support that without going to third party firmware (if it is even available for it) - and associated to the main wireless. After that plug the DirecTV box in to one of the LAN ports and you should be good to go.

The trickiest bit is going to be getting it in to wireless client mode and associated to the main router, the rest is easy.

If you can't get it to work, I have a wireless bridge that I will let you have cheap. I think it is a D-Link and I used to for a similar purpose, though I had a media player plugged in to it. Let me know.